Scientific Forecaster Discussion

Synopsis... low pressure crossing the Great Lakes will spread rain over the upper Ohio Valley region today. Precipitation may begin as freezing rain or a wintry mix...and will end by turning back to snow on Wednesday.

&&

Near term /until 6 PM this evening/... latest radar imagery showing weak echoes encapsulating the area...but copious dry air in place is keeping most precipitation at Bay. 12z sounding showing nearly a 50c dewpoint spread at 850mb. Until we erode this completely...virga will be present. The dry air looks to hold into the southeast ridges the longest as 925mb flow remains from the southeast. This will keep most areas south and east of Pittsburgh dry in downsloping flow until the afternoon when the flow veers to the south.

Have re-configured the winter weather advisories with the largest changes including cancelling the advisory in the ridges and speeding up the start time everywhere else. Still...with all the dry air in place and the lack of upstream radar activity...the probability of a widespread icing event has dropped.

Once the low-level flow veers to the south much warmer air should stream in and allow any remaining icing threat to end. This will happen south to north through the afternoon/evening. Have tailored the advisories to follow this transition. Tax

&&

Short term /6 PM this evening through Thursday/... Winter Storm Watch has been issued for counties across southeast ridges west to the southern half of the northern WV Panhandle to Noble County Ohio. This area appears to have best chance for 6 inches or more of snow late Wednesday PM into Thursday morning based on 12z models. Previous discussion follows.

With ongoing warm air and moisture advection into the evening...rain will continue fall area wide and temperatures will continue to increase until the associated cold front sweeps across the region starting shortly after midnight. Rain will remain fairly steady with the greatest amounts focused where middle- level convergence is greatest...along the I-80 corridor early in the evening and shifting south of the PA/WV border by Wednesday morning. With strong middle-level moisture transport into the area and upper level divergence associated with the right entrance region of a +170kt jet...portions of our forecast area could receive 1-1.5" of liquid through late Wednesday. This...combined with the potential for snow melt and ice on local creeks and streams...could cause high water issues for areas mainly south of Pittsburgh. An areal Flood Watch has been issued.

Colder air will begin to filter in Wednesday as the upper trough approaches from the west. Expecting temperatures to hold pretty steady through the day...which keeps the rain/snow line near Pittsburgh through the afternoon. By late evening temperatures will have fallen enough to transition rain to snow for all locations. Again there are questions surrounding how much moisture stays in our forecast area through Thursday morning as the Gulf of Mexico moisture feed kicks in and the upper level trough begins to kick the boundary off to our east. Potential for accumulating snow exists...mainly south and east of Pittsburgh where the deepest moisture holds. Confidence in snow totals at this point is fairly low...and will likely change as we move closer to mid-week.

&&

Long term /Thursday night through Monday/... overall...the long term period looks quiet with the passage of a couple of weak fronts Saturday night and then again late Monday. At this time...models are showing little moisture accompanying either of these systems. A slow moderation in temperatures is expected through the entire period.

&&

Aviation /19z Tuesday through Sunday/... advancing warm front should bring IFR a mix of snow...freezing rain and rain to kfkl and kduj through 21z or so...with spotty mixed precipitation to plain rain this afternoon elsewhere. IFR in rain overnight for all ports...then IFR continues Wednesday as cold front pushes south with rain mixing over to snow north to south.

Outlook.../Wednesday night through Sunday/... widespread restrictions are expected into Thursday as low pressure moves along a cold front. General VFR until a cold front brings possible restrictions Sunday.

&&

Hydrology... the combination of snow melt and developing rain is expected to cause significant rises on the cheat... Monongahela and youghiogheny river basins. These rises will aid in moving ice into areas where ice jams are known to develop. The rises will most likely begin Wednesday morning through Thursday afternoon. Uncertainty remains a factor on the amount of precipitation and where the axis of heaviest rain will fall.